Module 7 - Charts & Publications
Compass Rose on a Nautical Chart: True and Magnetic Bearings
Quick answer
A chart compass rose lets you measure true bearings from the outer ring and check magnetic variation from the inner magnetic information.
- Use the true ring for chartwork unless the question asks for magnetic or compass.
- Variation changes with year, so apply the annual change when required.
- Read bearings carefully from the direction of travel, not the reverse line.
Each chart has one or more compass roses printed on it. The outer ring shows True North (aligned with the chart grid). The inner ring shows Magnetic North, offset by the local variation. The variation value and year are printed on the rose, along with the annual change.
When using parallel rulers, walk them to the compass rose and read bearings from the appropriate ring — the outer ring for True bearings, the inner ring for Magnetic bearings.
Key points
- Outer ring = True North (chart grid)
- Inner ring = Magnetic North (offset by variation)
- Variation, date, and annual change printed on the rose
- Use the outer ring for True bearings in chartwork
Common mistakes
- Reading the wrong side of the compass rose.
- Using magnetic bearings when the chartwork answer should still be true.
- Ignoring annual change in variation on older charts.
Practise bearing conversions
Compass work links the chart compass rose to variation, deviation, and the CDMVT conversion process.